(a) Field of the Invention
This invention relates to EN2 gene as an oncogene, diagnostic and therapeutic uses thereof.
(b) Description of Prior Art
Breast cancer is one of the most frequent human malignancies in the Western world. The pathogenesis of this disease is thought to involve multiple genetic and epigenetic events. In spite of recent advances in the assessment of breast cancer risk, through the identification of crucial susceptibility genes (BRCA 1/2, PTEN, P53), they account for less than 5% of all breast cancer cases and may not be associated with the more commonly occurring sporadic breast cancers. The discovery of bona fide primary genetic lesions underlying sporadic breast cancer development remains a major challenge. This is due, at least in part, to the marked cytogenetic complexity seen in most breast cancers, precluding investigators from readily identifying primary causative genetic events in breast cell transformation.
A number of oncogenes and tumor suppressors have been associated with breast cancer. The c-MYC gene is amplified and/or overexpressed in a high proportion of human breast cancer, although the frequency of these alterations varies greatly. ErbB2 is also amplified and subsequently overexpressed in 20-30% of human breast cancers, and overexpression of ErbB2 is correlated with a poor clinical prognosis of both node-positive and node-negative tumors. The Cyclin D1 gene is amplified in 15-20% of human breast cancers. Although the basis for overexpression of MYC, Cyclin D1 and ErbB2 is often amplification of the gene, overexpression is also observed in the absence of amplification. As the oncogenes located at amplified chromosomal regions are rarely amplified in benign breast disease (Lizard-Nacol et al., 1995), they may represent late events in the multistep progression associated with the development of breast cancer.
In rodents, it has been possible to identify breast cancer-initiating oncogenes by the characterization of proviral integration sites of the mouse mammary tumor virus (MMTV). One such locus is Wnt-1 which, when overexpressed, leads to mammary hyperplasia and subsequent generation of adenocarcinomas. Although expression of WNT-1 itself has not been reported in normal or neoplastic human breast tissue; other WNT genes have been detected in subsets of human breast cancers. Wnt-1 encodes a secreted growth factor that initiates a signaling cascade which results in transcriptional activation mediated by β-catenin/Tcf complexes. β-catenin/Tcf-mediated transcription has also been implicated in human cancer, with some targets relevant to carcinogenesis identified such as c-MYC and cyclin D1. The observation that Wnt-1 is a mouse mammary oncogene and that the downstream mediator β-catenin is often stabilized in certain human malignancies fuels the ongoing search for relevant targets of this pathway, such as the Engrailed genes, that might be implicated in breast cancer.
The mouse Engrailed-1 (En-1) and Engrailed-2 (En-2) genes encode homeobox-containing transcription factors that are the murine homologs of the Drosophila segment polarity gene engrailed. En-1 is first expressed in the presumptive mid/hindbrain around 8.0 dpc and continues to be expressed, together with En-2, in overlapping patterns during midbrain development. Whereas En-2 expression during embryogenesis is restricted to the central nervous system (CNS) and branchiolar arches, En-1 is also expressed in two ventrolateral stripes in the hindbrain and spinal cord, in the dermomyatome, in the ventral ectoderm of the limb buds, and in sclerotomes. En-1 null mutants die shortly after birth with a large mid-hindbrain deletion and skeletal defects of the limbs, 13th rib and sternum, while En-2 mutants are viable but harbor reductions in cerebellar size (En-1, En-2: (Joyner et al., 1991)).